1. Field of the Invention
The present invention relates to a heat treating furnace and, more particularly, to a heat treating furnace capable of performing a heat treatment while protecting a measuring equipment and the like provided to the heat treating furnace.
2. Description of the Related Art
A furnace chamber of a heat treating furnace used for various heat treatments of, e.g., a semiconductor wafer, has a process tube for accommodating a semiconductor wafer as an object to be treated, a heater wire as a heating member surrounding the process tube, and a heat-insulating member arranged outside the heater wire.
In such a heat treating furnace, when, e.g., the interior of the process tube is to be kept at about 1,200.degree. C., the outer surface of the process tube is heated to about 300.degree. C. and has a rather high temperature. For this reason, it is required to prevent heat from being conducted to the outside of the furnace chamber to adversely affect a surrounding equipment.
Conventionally, each of Published Examined Japanese Utility Model Application No. 53-48589 and Published Unexamined Japanese Utility Model Application No. 49-39044 discloses a heat treating furnace in which a cooling fan is arranged around a furnace chamber to forcibly cool the furnace chamber.
As shown in FIG. 1, a terminal 11 and a junction box which houses a temperature measuring equipment are mounted around an outer tube 10 of the furnace chamber. In this case, the junction box 12 is mounted by an Al screw having good heat dissipation. Usually, the junction box 12 has a box-like main body 20 made of, e.g., stainless steel, and a terminal board 21 made of, e.g., a phenol resin, and housed in the box-like main body 20, as shown in FIG. 2. Compensating wires 22 are connected to the junction box 12 to constitute a thermocouple. A detecting section of the thermocouple is arranged inside the furnace chamber in order to measure a temperature in the furnace chamber. That is, as shown in FIG. 3, two compensating wires 30 form a detecting section 31 at one end each thereof and compensating contacts 21 on a terminal board 21 of the junction box 12, and are connected to a controller (not shown).
When the temperature in the furnace is stably kept at a processing temperature, heat is usually dissipated from the outer tube to the peripheral portion of the furnace body. Since the junction box is mounted on the outer tube, heat is conducted from the outer tube to the junction box through the screw which fixes the junction box. As a result, the ]unction box is heated. At the same time, the terminal board inside the junction box is also heated. In a conventional heat treating furnace, when the temperature in the furnace is 1,200.degree. C., the temperature of the outer tube becomes 280.degree. C., and the temperature in the junction box becomes about 102.degree. C.
The compensating contacts are formed on the terminal board of the junction box. Hence, when the temperature of the terminal board is increased, a temperature difference occurs. As a result, an actual temperature becomes higher than a set temperature by a value corresponding to the difference. Then, when a temperature profile and the like are input to the controller and temperature control is to be performed based on the temperature profile, accurate temperature control cannot be performed.
The heat-insulating temperature of the phenol resin as the material of the terminal board is about 85.degree. C. Therefore, when the temperature of the junction box exceeds this value, the terminal board may be damaged.
In this manner, in order to prevent various wirings and measuring equipments arranged around the furnace chamber from being adversely affected by the heat, the temperature around the furnace chamber is preferably set at about 50.degree. C. or less. With the conventional heat treating furnace, however, such high cooling performance cannot be expected. As the cooling performance is insufficient, the temperature around the furnace chamber cannot be lowered to 50.degree. C. or less. Accordingly, an adverse effect of the heat on the various wirings and measuring equipments arranged around the furnace chamber cannot be avoided.
The manufacture of a semiconductor wafer is performed in a quiet atmosphere in a clean room. For this purpose, convection of air and the like need be avoided as much as possible. However, in the conventional heat treating furnace of the forced air-cooling type, convection occurs and particles may scatter in the clean room.